Integration: Relational Databases

MySQL

Tables

The CREATE TABLE Statement

The CREATE TABLE statement is used to declare an MySQL table or view within an Omnidex Environment File. The Omnidex Environment File will contain a declaration for each MySQL table or view to be accessed, and will correlate all of the schema information between Omnidex and MySQL, including object names and datatypes. This statement can either be issued directly, or it can be extracted from MySQL using the EXTRACT statement as discussed in the previous section.

The following example compares the MySQL declarations with the Omnidex declarations.

MySQL CREATE TABLE Statement

create table STATES
       (STATE_CD                CHAR(2),
        DESCRIPTION             VARCHAR2(31),
        STATE_NUM               CHAR(2),
        REGION_CD               CHAR(2),
        COUNTRY_CD              CHAR(2),
        TAX_RATE                NUMBER(16,6));

Omnidex CREATE TABLE Statement

create table          "STATES"
 physical             "SIMPLE.STATES"
 (
  "STATE"             CHARACTER(2)   physical "STATE_CD",
  "DESCRIPTION"       STRING(31),
  "STATE_CODE"        CHARACTER(2)   physical "STATE_NUM",
  "REGION"            CHARACTER(2)   physical "REGION_CD",
  "COUNTRY"           CHARACTER(2)   physical "COUNTRY_CD",
  "TAX_RATE"          FLOAT
 )
 in                   "simple.xml";

In the Omnidex declaration, note that the PHYSICAL clause for table points to the MySQL syntax of user.table. Also note that the columns use the PHYSICAL clause to point to the underlying MySQL column name, and use Omnidex datatypes rather than MySQL datatypes.

Modifying Omnidex's View of the MySQL Data Objects

When Omnidex accesses a table, it only knows about the data objects that are declared in the Omnidex Environment File. It does not have an independent understanding of the MySQL environment. This allows administrators to shape the Omnidex Environment the way they want. Some of the opportunities this provides are:

Omnidex can have a controlled view of the MySQL database, limited to only the tables and columns that the application requires.
Omnidex tables can point to MySQL views, allowing an easy approach to reshaping the application's view of the data.
Omnidex can use different names for tables and columns by using the PHYSICAL clause in the TABLE or COLUMN sections of the CREATE TABLE statement to map to the underlying MySQL names.

for the MySQL tables and columns by using the respective PHYSICAL clause to

Omnidex columns can often be assigned datatypes that differ from the MySQL datatype. Character-class datatypes can be interchanged, allowing applications to easily receive the datatype that works best for its needs. Binary datatypes can be assigned to any of the integer or floating point datatypes; in fact, this is a necessity since MySQL's NUMBER datatype is only an internal datatype.
Omnidex tables can include Expression-based Columns, which are columns derived from a SQL expression rather than a specific column in the underlying database.

Referencing MySQL Views

Omnidex table declarations can reference MySQL Views. Omnidex will retrieve from the MySQL view just as though it is a table. MySQL Views can be used to provide different views of the data, appropriate for the application.

When referencing an MySQL view, it is necessary to declare a UNIQUE constraint. This requirement for the UNIQUE constraint is independent of any PRIMARY or FOREIGN constraints, discussed in the next page. The UNIQUE constraint tells Omnidex how to uniquely identify a row. When Omnidex retrieves individual rows, it will use this unique value; therefore, it is important that access to this column (or columns) be properly indexed in the underlying table.

MySQL CREATE VIEW Statement

create view STATES_VIEW 
 (
   CTRY_DESCRIPTION,
   CTRY_CAPITAL,
   STATE_CD,
   DESCRIPTION,
   STATE_NUM,
   REGION_CD,
   COUNTRY_CD,
   TAX_RATE
 ) as 
   select C.DESCRIPTION,
          C.CAPITAL,
          S.STATE_CD,
          S.DESCRIPTION,
          S.STATE_NUM,
          S.REGION_CD,
          S.COUNTRY_CD,
          S.TAX_RATE
   from   SIMPLE.STATES S, SIMPLE.COUNTRIES C
   where  S.COUNTRY_CD = C.COUNTRY_CD;